Note: Descriptions are shown in the official language in which they were submitted.
l~O~
ME~IOD FOR PRODUCTIQ~LOF MALEIMIDES
This invention relates to a method for the
production of maleimides. More particularly, this
invention relates to a method for the production of
maleimides by ring-closure imidation of maleinamic
acids.
Description of the Prior Art:
Maleimides are compounds useful as raw materials
for synthetic resins, medicines, and agricultural
chemicals. Researches after methods for their
production have long been under way. The most popular
method of them all effects the production of mal~imides
by the dehydration cyclization of maleinamic acids with
a dehydrating agent such as acetic anhydride. One
version of this method is disclosed in U.S. Patent No.
2,444,536. This method effects the production of
maleimides by causing maleic anhydride to react upon
amines thereby forming maleinamic acids and dehydration
cyclizing and, at the same time, imidating the
maleinamic acids in the presence of acetic anhydride
and sodium acetate. This method, however, has the
di~advantage that the imidation requires expensive
acetic anhydride to be used in at least an equivalent
relative to the maleinamic acid and the separation and
recovery of the ~ormed maleimide from the imidation
reaction solution necessitates use of a large volume of
water andl as the result, entails disposal of a large
amount of an acetic acid-containing effluent at great
expense. Thus, this method may well be called a too
expensive method for commercial production of
maleimides.
A method which has no use for such a chemical
dehydration agent as acetic anhydride is disclosed in
British Patent No. 1,041,027 and U.S. Patent No.
3,431,276. This method effects the production of
maleimides by thermally dehydrating and cyclizing
maleinamic acids in conjunction with a solvent such as,
for example, toluene, xylene, or
.' ~
1305~65
chlorobenzene having a boiling point exceeding 80C and
serving as a diluent and an~acid catalyst such as sulfur
trioxide, sulfuric acid, or ortho-phosphoric acid, and
distilling the system thereby causing azeotropic e~pulsion of
5 the consequently formed water in conjunction with the
solvent. As compared with the method which uses acetic
anhdyride, this method proves advantageous in that it does
not require use of a large amount of such an expensive
dehydrating agent as acetic anhydride and further that the
10 formed maleimides are separated and recovered with ease.
This method nevertheless has the disadvantage that the yield
of the imidation is low as compared with that obtainable by
the method using acetic anhdyride. This disadvantage is
logically explained hy a postulate that compared with the
15 method which effects the imidation by the use of acetic
anhydride, the method which effects the imidation by
performing thermal dehydration in the specific solvent as
described above involves a high reaction temperature and,
therefore, tends to induce side reactions and inevitably
20 manages to produce maleimides abounding with impurities and
further that since maleimdies are thermally unstable, the
maleimides produced at all are degenerated during the course
of the reaction. Further, as a commercial process, this
method is not ecconomically satisfactory, because it requires
25 to use an expensive acid catalyst in a relatively large
amount and, moreover, produces the maleimides in a low yield.
There is another method which, as disclosed in
Japanese Patent Laid-Open SHO 53(1978~-68,700 and Japanese
Patent Publication SHO 57(1978)-42,043, comprises causing
30 maleic anhydride to react on amines in the presence of an
organic solvent thereby forming maleinamic acids and
subjecting the maleinamic acids as held in a state not
isolated from the reaction system to dehydration and
cyclization in the presence of such an aprotic polar solvent
35 as dimethyl formamide or dimethyl sulfoxide and an acid
catalyst. By this method, there is offered recognizable
~30S96i5
improvement in yield as compared with the second method
described above. This method, however, has these
disadvantages, that the cost of production of maleimides is
high because expensive and highly toxic aprotic polar solvent
5 such as dimethyl formamide is used in a large amount, that
the solvent such as dimethyl formamide is degenerated by the
action of an acid catalyst used in the reaction and,
therefore, the solvent is lost greatly, and that since the
aprotic polar solvent used in the reaction has a high boiling
10 point, the solvent is removed from the produced malimides
with great difficulty.
Japanese Patent Laid-Open SHO 54(1979)-30,155
discloses a method for producing an oligoimide by using, as a
catalyst, a mixture of an inorganic or organic
15 acid-containing acid with a quaternary ammonium salt of the
acid. The quaternary ammonium salt which is used as mixed
with an acid catalyst in this method, however, is an ammonium
salt of the nitrogen atom of which has been at least
disubstituted. Specifically, this is an expensive interphase
~0 catalyst such as dimethyldialkyl ammonium methane sulfonate
or tetraoctyl ammonium methane sulfonate. The method, thus
necessitating use of such a compound as indicated aobve, is
inevitably judged to be an expensive approach. For this
method to maintain a highly satisfactory yield of imidation,
25 however, it is essential .that the reaction should be
continued with the ratio of the acid catalyst to the
quaternary ammonium salt rigidly controlled within a certain
range. When the catalyst which has been used once in the
reaction is used again, the imidation cannot be obtained in a
30 highly satisfactory yield because the ratio is varied in the
presence of the used catalyst. An effort to attain efficient
reuse of the used catalyst~ therefore, entails as a problem
the fact that the management for maintenance of catalytic
activity as by subjecting the used catalyst to purifying and
35 readjusting treatments calls for immense labor.
..
,
:
~31~59~5
Japanese Patent Laid-Open SH0 60(1985)-109,562
discloses a method for the production of monomaleimide
by the cyclizing imidation of maleinamic acid in a mixed
solvent containing a nonpolar solvent such as toluene or
xylene and a polar solvent such as dimethyl sulfoxide or
N-methyl pyrrolidone in a specific ratio in the presence
of an acid catalyst such as p-toluenesulfonic acid or
m-toluenesulfonic acid and a mixed catalyst containing
the acid catalyst and an ammonium salt such as, for
example, the salt thereof with maleinamic acid. In this
method, however, since the acid catalyst and the polar
solvent in the mixed solvent react with each other to
form a complicate complex (which is widely variable with
the ratio of the amounts of the two compounds and the
temperature, for example), it is the complicate catalyst
system composed of the complex ~ust mentioned, the acid,
and the salt that substantially produces a catalytic
activity. Thus, the yield of the imidation is affected
to a great extent by the composition of the three
components mentioned above. When the reaction is
carried out batchwise, it does not entail any
appreciable disadvantage. When the reaction is carried
out in such operation system as require the catalyst
and the solvent to be used in a recycling manner,
however, it entails various drawbacks. To be specific,
this method renders the selection of reaction conditions
compllcate because the amount of the aomplicate complex
produced owing to the use of the polar solvent is varied
and the catalyst is varied in quality from one batch to
another. This is equivalent to a statement that the
method under discussion has the di~advantage that it is
unfit for a continuous reaction.
Thi~ invention 18 directed towards the provision of
an improved method for the production of maleimides of
high purity in a high yield by a safe and simple
~:
~ i
. ~
,.,, ,,,, ,,. .~.. ~:, .,
~30S965
procedure, which may be effected easily by a continuous
reaction.
In accordance with one aspect of the present
invention, there is provided a method for the
production of a maleimide by dehydration and cyclization
of a maleinamic acid obtained by the reaction of maleic
anhydride with an amine, which method is characterized
by effecting ring-closure imidation of the maleinamic
acid by heating this acid in a water-insoluble or
water-immiscible inert organic solvent in the presence
of a catalyst comprising a mixture of an amine salt
produced from the amine as the raw material for the
production of maleimide and an inorganic or organic acid
and the inorganic or organic acid.
We have long been continuing a study on the
reactions for synthesis of maleimides. Particularly, we
have devoted our study to development of a catalyst for
use in the ring-closure imidation reaction. The study
has resulted in a finding that a mixture of an amine
salt with an acid and the acid manifests a catalytic
activity of unusually high selectivity on the cyclizing
imidation reaction. This invention has been perfected
a~ the result.
In the light of the long aherished theory that the
pre~ence of an oxygen-containing acid is indispensable
to the reaction of ring-closure imidation, it is
literally an amazing fact that the use of the amine salt
produced by the neutralization brings about an unusually
high catalytic activity in the reaction of ring-closure
imidation.
The method for the production of an maleimide
according to this invention reside~ in causing
dehydration and ring-closure imidation of a maleinamic
acid obtained by the reaction of maleic anhydride with
an amine to be carried out in a water-insoluble or
water-immiscible inactive organic
,~'
130S9t~5
solvent in the presence of a mixture of an amine salt
obtained from the amine and an inorganic or organic acid with
the inorganic or organic acid.
The maleinamic acids to be used in this invention
5 are easily obtained generally by the reacticn of primary
amines with maleic anhydride. They are desired to be
compounds represented by the following general formula I.
CH - C - OH
10 ~ (I)
~H - C - NH - R
wherein R denotes a member selected from the class consisting
of alkyl of 1 to 20 carbon atoms, phenyl, benzyl, cyclohexyl,
15 pyridyl, and quinolyl groups, and the same groups as
mentioned above and possessed of halogen, carboxyl, or nitro
substituents; providing that said alkyl groups or phenyl
groups are more desirable than the other groups mentioned.
Examples of the primary amine particularly useful
20 as the raw material for the maleinamic acid in this invention
include methylamine, ethylamine, n-propylamine,
i~opropylamine, n-butylamine, sec-butylamine, isobutylamine,
tert-butylamine, n-hexylamine, n-dodecylamine, allylamine,
benzylamine, cyclohexylamine, aniline, nitroaniline,
25 aminomonochloroaniline, dichloroaniline, toluidines,
xylidines, and ethylanilines.
Synthecis of a maleinamic acid proceeds virtually
stoichiometrically. For example, the maleinamic acid can be
synthesized by causing the amine in an amount of 0.8 to 1.5
re~o~
O 30 mols, preferably 0.9 to 1.2 mols, to rtaacb upon each mol of
maleic anhydride.
The organic solvent to be used in the present
invention is desired to be capable of permitting the water
formed by the reaction of dehydration and cyclization to be
35 expelled from the reaction system through azeotropic
distillation therewith, insoluble or immiscible in water,
,. . .
, .
130S9~5
inert, and incapable of participating in the reaction.
Examples of the organic solvent meeting this description are
benzene, toluene, oil fractions boiling at temperatures in
the range of 50 to 120 C, xylenes, ethyl benzene, isopropyl
5 benzene, cumene, mesitylene, tert-butyl benzene,
pseudo-cumene, trimethyl hexane, octane, tetrachloroethane,
nonane, chlorobenzene, ethyl cyclohexane, oil fractions
boiling at temperatures in the range of 120 to 170C,
m-dicyclobenzene, sec-butyl benzene, p-dichlorobenzene,
10 decane, p-cymene, o-dichlorobenzene, butyl benzene,
decahydronaphthalene, tetrahydronaphthalene, dodecane,
naphthalene, cyclohexyl benzene, and oil fractions boiling at
t temperatures in the range of 170 to 250C. From th~e
standpoint of enabling this reaction to proceed ~Smmoth~
15 under satisfactorily economic conditions, the amount of this
solvent to be used in the reaction is in the range of 1 to 20
times, pre~erably 3 to 7 times (by volume), the amount of
maleinamic acid.
Further, the solvent is selected on the condition
20 that it should possess a boiling point suiting the prevalent
reaction conditions in due consideration of the solubility of
the maleimide, price, and ease of handling. When the
separation of the maleimide and ~he solvent after completion
of the reaction demands an important consideration, there are
25 times when the reaction performed by the use of a solvent of
a low boiling point under application of pressure may prove
to be more advantageous.
As a catalyst, a mixture of an amine salt with an
inorganic or organic acid is used. This mixed catalyst
30 produce~ desirable results when the amine salt content
thereof at least exceeds 40 mol%, preferably falls in the
range of 50 to 80 mol%.
As the amine salt, there is used the amine salt
which i~ obtained by subjecting an inorganic or organic
35 monobasic or polybasic acid such as p-toluenesulfonic acid,
orthophosphoric acid, metaphosphoric acid, pyrophosphoric
;~
.. ~, . . . . . .
,
. .
~30S965
acid, benzene sulfonic acid, or trichloroacetia acid with an
amine as a raw material for the production of maleimide.
This amine salt is preferred to be such that at least one of
the protons of the monobasic acid or polybasic acid is
5 substituted with an amine.
The amount of the catalyst to be used falls in the
range of 2 to 400 mol%, preferably 20 to 200 mol%, as an acid
component contained in the catalyst, based on the amount of
the maleinamic acid, wherein the acid component contained in
10 the catalyst means both an acid component which constitutes
the amine salt and free acid.
The mixture of the amine salt with the acid is
insoluble in the organic solvent to be used in the present
invention. In the reaction system, therefore, this liquid
lS catalyst assumes a state separated into the two layers, an
organic layer and an inorganic layer. This state remains
intact during and after the reaction. Moreover, the amine
salt or the mixture thereof with an acid serving as the
catalyst remains substantially unchanged before and after the
20 reaction. The catalyst system of this nature itself,
therefore, can be utilzied in situ in the next cycle of
reaction without being recovered and refined in the meantime.
When this catalyst layer is to be used in the next
cycle of reaction, the organic layer and the catalyst layer
25 existing at the end of the reaction may be separated one from
the other at a temperature in the range of 120 to 250C, and
the catalyst layer consequently recovered may be put to use
directly in the next cycle of reaction. Otherwise, the
recovered catalyst layer may be diluted with 5 to 20 % by
30 weight of water to lower both temperature and viscosity so to
be added to the reaction system for the next cycle of
reaction for the sake of convenience of handling.
There are times when the reaction can be carried
out, a~ di3closed in U.S. Patent No. 4,623l734, in the
35 presence of a metal-containing compound and a stabilizer.
The metal-containing compound to be used in Chis case is
- 8 -
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-"` 13059tl~i
selected from among oxides, acetates, maleates, succinates,
nitrates, phosphates, chlorides, and sulfates of at least one
metal selected from the group consisting of zinc, chromium,
palladium, cobalt, nickel, iron, and aluminum. Among other
5 compounds enumerated above, zinc acetate proves to be
particularly effective. The amount of the metal-containing
compound to be used is in the range of 0.005 to 0.5 mol%,
preferably 0.01 to 0.1 mol%, as metal, based on 1 mol of the
maleinamic acid.
Examples of the stabilizer to be used
advantageously herein include methoxy benzoquinone,
p-methoxyphenol, phenothiazine, hydroquinone, alkylated
diphenyl amines, methylene blue, tert-butyl catechol,
tert-butyl hydroquinone, zinc dimethyldithiocarbamate, copper
15 dimethyldithiocarbamate, copper dibutyldithiocarbamate,
copper salicylate, thiodipropionic esters,
mercaptobenzimidazole, triphenyl phosphite, alkylphenols, and
alkylbisphenols.
The stabilizer plays the part of enabling the
20 maleimide which is produced by the reaction of imidation to
retain stably during the course of the imidation without
being degenerated at the elevated temperature of the
reaction.
Concerning the amount of the stabilizer to be
25 added, the addition of the stabilizer in a minute amount is
not sufficiently effective and the addition thereof in an
unduly large amount is undesirable because it entails the
drawback that the excess of stabilizer finds its way into the
final product. The amount of the stabilizer to be
30 effectively used is in the range of 0.005 to 0.5 mol~,
preferably 0.05 to 0.3 mol%, based on 1 mol of the maleinamic
acid.
Regarding the manner of working out the present
invention, first maleic anhydride prepared as a solution in
35 an organic solvent and an amine compound added thereto are
allowed to react with each other at a temperature not
30596S
exceeding 150C, preferably falling in the range of 30 to
120C, for a period of 15 to 120 minutes, preferably 30 to
60 minutes to produce maleinamic acid. Then, the reaction
system in which the maleinamic acid is left unisolated, the
5 catalyst or the catalyst layer separated from the reaction
system of the preceding cycle of reaction, and optionally the
metal-containing compound and/or the stabilizer are combined
and heated at a temperature in the range of 120 to 250C,
preferably 130 to 220C, for a period in the range of one
10 hour to 15 hours, preferably 3 to 7 hours to effect the
reaction in a continuous pattern with the formed water
expelled from the system through azeotropic distillation or
to effect the reaction in a batchwise pattern with the
expulsion of the formed water carried out at the end of the
15 reaction. As the result, the maleimide is produced in a high
yield.
The maleimide which is consequently obtained is a
compound represented by the general formula II, for example.
1l
CH - C ~
¦ N - R (II)
CH - C ~
I
O
wherein R has the same meaning as defined above. Typical
25 examples of the maleimides include N-methyl maleimide,
N-ethyl maleimide, N-n-propyl maleimide, N-isopropyl
maleimide, N-n-butyl maleimide, N-sec-butyl maleimide,
: N-tert-butyl maleimide, N-n-hexyl maleimide, N-n-dodecyl
maleimide, N-allyl maleimide, N-benzyl maleimide,
30 N-cyclohexyI maleimide, N-phenyl maleimide, N-nitrophenyl
maleimide, N-hydroxyphenyl maleimide, N-methoxyphenyl
maleimide, N-ethoxyphenyl maleimide, N-monochlorophenyl
; maleimide, N-dichlorophenyl maleimide, N-monomethylphenyl
maleimide, N-dimethylphenyl maleimide, and N-ethylphenyl
-- 10 --
130~65
maleimide. Of course, the maleimides which this invention is
intended to embrace are not limited to the examples cited
above.
This invention which has been described above
5 brings about the following advantages.
(1) The present invention permits a maleimide of high
purity to be produced in a high yield, because mixture of the
amine salt formed by the reaction of neutralization of the
amine as the raw material for the production of the maleimide
10 with an inorganic or organic monobasic or polybasic acid with
an acid possesses a catalytic activity of high selectivity on
the reaction of cyclizing imidation.
(2) The cost of the catalyst can be substantially
disregarded because the mixture used as the catalyst is
15 stable enough to be used time and again in the successive
cycles of reaction.
(3) Since the catalyst is used repeatedly, there is
substantially no need for the treatment otherwise required to
be given to the used catalyst for the eventual prevention of
20 environmental pollution. Since the reaction system,
therefore, can be operated in a closed pattern, there is
virtually no possibility of the environment being polluted
with discarded catalyst.
As described in (1) through (3), this invention
25 permits a maleimide to be easily produced inexpensively and
safely.
Now, the present invention will be described more
specifically below with reference to working examples.
-- 11 ~
13~65
Example 1
In a Meyer's flask~having an inner volume of 300
ml, lOOg of orthoxylene and 60 g of orthophosphoric acid were
dispersed. Then, the Meyer's flask was kept cooled in a
5 water bath and 37 g of cyclohexylamine was added dropwise
thereto to obtain a slurry solution of a white mixed catalyst
of monocyclohexylamine salt of orthophosphoric acid and
orthophosphoric acid in xylene. The amine salt content in
the mixed catalyst was 60.9 mol%.
Separately, a flask provided with a condenser
incorporating therein a water separator, a dropping funnel,
and a stirrer was charged first with 100 g of arthoxylene and
then with 100 g of maleic anhydride and heated until the
inner temperature thereof reached 100C, t~ dissolve the
15 maleic anhydride.
Then, a solution of 100 g of cyclohexylamine in 600
g of orthoxylene was added dropwise while in a stirred state
over a period of one hour, to synthesize a slurry solution of
N-cyclohexyl maleinamic acid in orthoxylene.
Thereafter, this slurry solution and the mixed
slurry solution of amine salt and orthophosphoric acid (the
amount of the mixed catalyst corresponding to 60.7 mol%,
based on maleinamic acid) and 0.1 g of copper dibutyl
dithiocarbamate added thereto were left reacting for seven
25 hours by being heated and stirred at 143C, with the water
formed by the reaction continuously expelled by distillation
in ~ombination with orthoxylene from the reaction system in
the meantime. After the reaction was completed, the catalyst
layer separated in a lower layer from the reaction solution
30 at 143C was removed.
Subsequently, the reaction solution was cooled to
60C and washed by being stirred with 100 g of water for 30
minutes, to separate the water layer. This operation was
repeated twice. The organic layer consequently formed was
35 distilled under a vacuum of 10 mmHg (abs) to expel
orthoxylene.
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Then, the contents of the flask and 0.3 g of copper
dibutyl dithiocarbamate newly added were left standing under
a vacuum of 5 mmHg (abs) at a flask inner temperature of 130
to 150C for 30 minutes, to effect distillation of
5 N-cyclohexyl maleimide. As the result, there were obtained
171 g of bright white crystals of N-cyclohexyl maleimide.
The purity of this product was 99.8 % by weight and the yield
thereof was 94.4 mol% based on cyclohexylamine used as the
raw material.
Thereafter, a reaction was carried out by
faithfully following the procedure described above, excepting
the catalyst layer separated from the reaction system of the
preceding cycle of reaction was used instead. Consequently,
there were obtained 171 g of bright white crystals of
15 N-cyclohexyl maleimide. The purity of this product was 99.8
% by weight and the yield thereof was 94.4 mol% based on
cyclohexyl amine used as the raw material.
Example 2
In a Meyer's flask having an inner volume of 300
20 ml, 100 g of p-cymene and 100 g of orthophosphoric acid were
dispersed. Then, the Meyer flask was kept cooled in a water
bath and 56 g of n-butyl amine was added drowpwise thereto,
to obtain a white mixed ~lurry solution of n-butylamine salt
of orthophosphoric acid and orthophosphoric acid. The amine
25 content in this mixed catalyst was 75.0 mol~.
Separately, a reactor was prepared by furnishing a
glass flask having an inner volume of 1 liter with a
thermometer, a stirrer, and a water separator.
Then, a solution of 53 g of powdered maleic
30 anhydride in 50 g of p-cymene was placed in the reactor.
Subsequently, the inner temperature of the reactor was
adjusted to 130C and a solution of 40 g of n-butyl amine in
400 g of p-cymene was added thereto piecemeal in a dropwise
manner over a period of 30 minutes, to synthetize a solution
35 of N-(n-butyl)maleinamic acid.
- 13 -
r
' ~T
0S96~
The solution thus obtained and the slurry solution
of mixed catalyst (the amount of mixed catalyst corresponding
to 186.5 mol% based on the maleinamic acid), 0.034 g of zinc
acetate, and 0.065 g of p-methoxy phenol added thereto were
5 left reactinq at a temperature of 180C for three hours, with
the formed water continuously expelled in combination with
p-cymene form the reaction system in the meantime. After the
reaction was completed, the reaction solution weighed 620 g.
The concentration of N-(n-butyl) maleimide in this reaction
10 solution was 11.5 % by weight. The yield of the maleimide
was 85.1 mol3 based on n-butylamine used as the raw material.
A reaction was carried out by faithfully repeating
the procedure described above, excepting the catalyst layer
separated from the reaction system of the preceding cycle of
15 reaction was used instead, to obtain 625 g of a reaction
solution. The concentration of N-(n-butyl) maleimide in this
reaction solution was found by analysis to be 11.6 % by
weight. The yield was 86.5 mol%.
Example 3
In a Meyer's flask having an inner volume of 300
ml, 60 g of orthopho~phoric acid was placed. Then, this
Meyer's f lask was kept cooled in a water bath and 46 g of
cyclohexylamine was added dropwise thereto, to obtain a
viscous slurry solution of mixed catalyst of
25 cyclohexyl-monoamine of phosphoric acid and phosphoric acid.
The content of amine salt in this mixed catalyst was 75.8
mol%.
Separately, a glass autoclave having an inner
volume of 1 liter and provided with a thermoneter, a
30 condenser, a dropping funnel, and a stirrer was charged first
with 100 g of orthoxylene and then with 100 g of maleic
anhydride and then heated until the inner temperature of the
flask reached 100C, to effect dissolution of the maleic
anhydride.
- 14 -
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,, .. , ," ,.~, .. . . .
1305965
Subsequently, a solution of 100 g of
cyclohexylamine in 400 g of orthoxylene was added dropwise
thereto while in a stirred stste over a period of 30 minutes,
to synthesize a slurry solution of N-cyclohexyl maleinamic
5 acid in the solvent.
Then, the slurry solution and the slurry of mixed
catalyst (the amount of the mixed catalyst corresponding to
60.7 mol% based on the maleinamic acid added thereto were
left reacting at an inner of 152C for three hours in a
10 closed system without expulsion of the formed water. In the
reaction system, the inner pressure was 1.2 atm at the outset
of the reaction and was 7.0 atm after three hours of the
reaction.
After the reaction was completed, the inner
15 temperature was adjusted to 130C and then the inner pressure
was allowed to fall to normal atmopsheric pressure. The
reaction product was removed from the autoclave and left
standing at rest. Consequently, the reaction solution was
separated clearly into two layers, i.e. an organic layer and
20 a catalyst layer. The organic layer weighed 660 g. The
content of N-cyclohexyl maleimide in this organic layer, on
analysis by gas chromatography, was found to be 24.6 % by
weight. The yield of this maleimide was 89.8 mol%, based on
cyclohexylamine used as the raw material.
Subsequently, a reaction was carried out by
faithfully repeating the procedure described above, excepting
the mixed catalyst layer of amine salt and acid separated
from the reaction system of the preceding cycle of reaction
was used instead. Consequently, there was obtained 664 g of
30 an organic layer. The content of N-cyclohexyl maleimide in
this organic layer was 24.5 % by weight. The yield thereof
was 90.0 mol% based on cyclohexylamine used as the raw
material.
13~5g6~
Control 1
To a solution of 98 g of maleic anhydride in 500 g
of toluene, 99.2 g of cyclohexylamine was added dropwise at a
temperature in the range of 50 to 70C while in a stirred
5 state. After the dropwise addition, the resultant mixture
was stirred for two hours. Consequently N-cyclohexyl
maleinamic acid was obtained. Then, the reaction solution
and 14 g of methanesulfonic acid, 8.7 g of methanesulfonic
acid-N-cyclohexyl maleinamate, and 15 g of N-methyl
10 pyrrolidone added thereto were left reacting at 115C for 3.5
hours in a refluxed state, with the formed water continuously
expelled from the reaction system through azeotropic
distillation with toluene.
Then, the resultant reaction solution was caused to
15 react with 15 g of acetic anhydride for 30 minutes, cooled to
60C, and filtered to be deprived of insoluble impurities,
the catalyst, and unaltered N-cyclohexyl maleinamic acid.
Subsequently, the filtrate was washed by 30 minutes' stirring
with 200 g of water to separate the water layer. This
20 operation was repeated twice. The organic layer consequently
obtained was distilled under a vacuum of 30 mmHg (abs) to
expel toluene. As the result, there was obtained 172g of a
brown solid containing cyclohexyl maleimide. By the GPC
analysis, the N-cyclohexyl maleimide was found to be 10.0 %
25 by weight and the yield ~f N-cyclohexyl maleimide was to be
9.6 mol~, based on cyclohexylamine. When the reaction
~olution was analyzed by gas chromatography, the results
showed the same yield.
Control 2
A reaction was carried out by faithfully repeating
the procedure of Control 1, excepting 73 g of n-butylamine
was used in the place of cyclohexylamine, 14 g of
methanesulfonic acid and 8.4 g of tributylamine salt of
methanesulfonic acid were used as a reaction catalyst, and
35 dimethyl formamide was used in the place of N-methyl
- 16 -
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- ~30$965
pyrrolidone as the polar solvent. Consequently, there was
obtained 151 g of a brown oily liquid containg N-n-butyl
maleimide.
By the GPC analysis, the content of N-n-butyl
S lmaleimide was found to be 13.4 ~ by weight and the yield
thereof to be 13.2 mol% based on N-butylamine used as the raw
material.
When the reaction solution was washed with water
and analyzed by gas chromatography, the results showed the
10 same yield.
Control 3
A solution of 43.1 g of maleic anhydride in 331.8 g
of chlorobenzene and 39.7 g of cyclohexylamine added thereto
were left reacting at 40C for one hour.
The slurry solution of N-cyclohexyl maleinamic acid
consequently obtained and 12 ml of dimethyl acetamide and 2 g
of trichloroacetic acid added thereto were left reacting at
135C for six hours, with the formed water continuously
expelled in combination with the solvent from the reaction
20 system in the meantime.
At the end of the reaction, there was obtained 402
g of reaction solution. This reaction solution, on analysis
by gas chromatography, was found to contain 2.2 % by weight
of N-cyclohexyl maleimide.
The yield of this N-cyclohexyl maleimide was 12.3
mol%, based on cyclohexylamine used as the raw material.
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